This thesis conducts a comprehensive exploration of high amylose starches (HASs), focusing on their structure,thermal characteristics, resistance to hydrolysis, and the interactions with digestive enzyme.

A novel interfacial kinetics approach, originally designed for cellulose degradation, was adapted for the analysis on degradation of starch granules. This approach combines conventional and inverse MichaelisMenten (M-M) kinetics with Langmuir adsorption isotherm analysis to characterize effective (attack sites) and non-effective binding sites on starches of various structures. Initially, maize starches with amylose contents (AC) ranging from 0–72% were investigated, using glucoamylase (GA) as the enzyme model. The investigation unveiled that the high enzymatic resistance observed in high amylose maize starch can be attributed to lower density of attack sites on the surface of starch granules. This resistance becomes more pronounced during digestion as these attack sites diminish due to amylose reorganization.

Subsequently, eight diverse HASs from different botanical sources, including maize, wheat, barley, and potato, with amylose (AM) contents ranging from 34.4% to 97.3%, were analyzed. Significant structural differences were identified among these HAS varieties. Wheat and barley starches exhibited reduced order degree of lamellar and crystalline structures, along with rugged surfaces. These characteristics were attributed to the presence of short amylopectin (AP) chains or “AM-like” chains and long amylose chains. In contrast, maize and potato starches exhibited more organized crystalline structures with smooth surfaces. Notably, the thermal resistance was not directly linked to apparent amylose content (AAC) but influenced by degree of branching and V-type crystals. The degree of branching played a significant role in shaping the thermal properties of HAS, with a positive impact on the gelatinization enthalpy and a negative effect on the gelatinization temperature. Furthermore, the presence of V-type crystals was linked to higher gelatinization temperatures.

An examination of the structures of eight HAS samples alongside their post-digestion residuals (resistant starch, RS) highlighted that the percentage of smooth-surfaced granules of HAS, which is possibly linked to the formation of large blocklets through B-type crystalline polymorphism, and locally organized structures with a high double helix content, played pivotal roles in determining their resistance to enzymatic hydrolysis. Higher RS content was associated with starch granules having more smooth surface and abundant double helices, while lower RS content was found in starches with rougher textures and more amorphous regions. The resistant starch in HAS likely comprises both the original resistant starch structure and the reorganized structure that occurs during digestion. Notably, longer AM in wheat and barley underwent significant molecular reorganization during digestion, resulting in enhanced enzymatic resistance and the formation of enhanced resistant starch (eRS), which exhibited limited hydrolysis (~10%) during subsequent digestion.

The application of interfacial enzymatic kinetics in different HAS revealed variations in the interactions between density of attack sites and binding sites, and turnover rates (kcat) for different HASs and GA. High amylose potato starch, which displayed the smoothest surface, showed the lowest density of binding sites, whereas for other HAS samples, density of binding sites seems not to be the limiting factor for hydrolysis of GA. Instead, density of attack sites played a more crucial role. While all HAS samples exhibited limited attack sites, their varying levels of hydrolysis resistance primarily stemmed from the different affinities GA exhibited toward these starches, resulting in distinct kcat for each starch. HAS with larger particle sizes and less ordered surface structures, such as amylose only barley starch (AOBS), exhibited optimal affinity from GA, resulting in higher kcat value. Additionally, the density of attack sites was higher for HAS samples with longer side chains on the granular surface. The increased density of binding sites while decreased density of attack sites for HAS RS (high amylose resistant starch) might due to amylose reorganization, leading to enhanced hydrolytic resistance. An exception was high amylose potato starch, which exhibited reduced hydrolytic resistance.

In summary, this thesis has deepened understanding of the structure, thermal properties, and enzymatic resistance of HAS. Furthermore, interfacial kinetics can be a valuable tool in applications of starches, such as starch modification and the degradation of starch-based biocomposites.